i want to create empty texture slots so i can add texture images later on
First you must make sure a material is assigned to your mesh. Then in the texture tab you can add as many textures as you please to the list at the top. Under the "Image" section you can open a file browser window to choose your textures.


If no texture is selected it should just show a big button to open an image.

You can then mix the textures or make them affect different properties, like normal and specular under the "Influence" section.